A margin, also called a circular land, is understood to mean guide portions on workpieces and cutting tools, such as e.g. boring and milling tools. The margins are crucial for the surface quality of a wall of a bore, for example. In other words, a margin decisively influences roughness measured values such as roughness depth, for example of a bore wall. To illustrate what is meant by a margin, reference is made to FIG. 9.
FIG. 9 shows a deep-drilling tool with guide pads 1 and 2, a chip space 3 and a cutting edge 4. In the enlarged detail according to FIG. 9, the guide phase 5 on an edge of the guide pad 2 can be seen. The guide phase 5 has a complex geometry with a relief 6.
Since the guide phase is of great importance for the surface quality of a workpiece to be machined by the cutting tool, the margins have to be produced with high precision. Particularly the fabrication of the margins with high precision has proved to be difficult in practice, because of the complex geometries of the margins with reliefs and undercuts.
Hitherto, margins have been formed on workpieces by means of suitable cylindrical grinding machines. With such a cylindrical grinding machine, variations in the geometries of the circular land or the margin are possible only to a very limited extent, so that the margins produced with previous methods have mostly to be formed cylindrically and cannot have a clearance angle for example.
To produce the margin or circular land, the workpiece to be machined is clamped in the cylindrical grinding machine and subsequently machined by the latter. Since the margins have to be produced with high precision and dimensional accuracy, intermediate inspections, i.e. regular inspection measurements, are necessary. For these, the workpiece—the subsequent cutting tool—has to be unclamped and removed from the cylindrical grinding machine, in order to be able to be clamped in a separate measuring device for the measuring. In other words, the workpiece has to be reclamped for manual measurement during intermediate and final inspections. If further grinding operations are necessary, the workpiece is subsequently clamped in the grinding machine once again, in order to continue the grinding process. The reclamping of the workpiece has an adverse effect on the dimensional accuracy and accuracy to shape of the margin.
Since a grinding wheel is used for grinding the margin, on feed movements of the grinding wheel it is always necessary also to take account of the erosion on the grinding wheel itself, which can have a considerable adverse effect on the production time and the production precision. Particularly in the case of long workpieces, for example reamers, which are to be provided with a margin, the compressive force applied to the workpiece by the grinding with a cylindrical grinding machine has, moreover, an adverse effect on the form and shape of the workpiece.
Generally, devices for machining workpieces by means of laser beams are known from the prior art and disclosed, for example, in the document DE 40 40 554 A1. The machine tool disclosed in this document comprises a housing which is mounted on a machine column and in which a guide tube is arranged so as to be longitudinally displaceable. At the rear end part of the housing is mounted a laser unit, the laser beam of which passes through a focusing optical system and exits from a nozzle head, in which means for supplying at least one fluid to the central exit opening of the laser beam are provided. For laser machining a workpiece, the guide tube is moved horizontally until a nozzle head is immediately in front of the workpiece surface to be machined. The laser unit is activated to perform the removal of material in layers, while the work table performs a combined horizontal movement and a swivelling movement about a vertical axis. To perform cutting machining operations on the workpiece, the laser head is replaced by a cutting tool by means of a tool changer.
The device for machining a workpiece by means of laser beams known from the prior art is, however, not suitable for forming a margin on a workpiece or on a cutting tool, because it is designed for producing cavities in solid workpieces. Such a margin is to be formed on a circumferential surface of the workpiece and has a complex geometry which is not comparable with a simple cavity.
Furthermore, laser machining devices for producing a rotationally symmetrical tool from a blank are known from the prior art and disclosed, for example, in DE 10 2010 011 508 A1.
The laser machining device according to DE 10 2010 011 508 A1 has a control device and a positioning device via which a relative position between a laser head and the tool blank can be set and changed. Via a deflecting device, the laser beam impulses produced by the laser are directed in the region of a pulse area onto the surface of the blank. To produce the cutting edges or chip grooves on the tool blank, the control device specifies for the deflecting device a pulse path for arranging successive impact locations. The course of the pulse path depends on the shape of the pulse area and, in a rectangular pulse area, has a meandering course, which is composed of straight-line partial courses. Pulse areas of round, elliptical or curved shape are also possible. Starting from a starting point, the laser beam impulses are placed along the pulse path until an end point of the pulse path is reached. Upon reaching the end point, a reset movement takes place in the deflecting device and the laser beam impulses are then again placed on the pulse path beginning at the starting point, so that a material removal occurs layer-by-layer. While via the deflecting device, a two-dimensional spatially limited pulse area is machined, the positioning device causes at the same time a relative movement of the pulse area on the surface of the blank. To produce a chip groove or a cutting edge on the blank, the material is removed layer-by-layer in a plurality of removal layers by the movement of the pulse area over the surface of the blank, so that the desired chip groove is formed after considerable material removal.
In the case of the laser machining device disclosed in the document DE 10 2010 011 508 A1, the material is removed layer-by-layer in a plurality of removal layers by the movement of the pulse area over the surface of the blank. During this, the laser beam impulses follow the course of a specified pulse path. Upon reaching an end point of the pulse path, a reset movement takes place, and the next material layer to be removed is removed starting from the starting point of the pulse path.
The laser machining device disclosed in this document removes material layer-by-layer via repeated following of a specified pulse path and in each case always machines the same specified region—a region of a chip groove or a cutting edge—on the workpiece until its completion. The laser machining device according to DE 10 2010 011 508 A1 does not provide for producing a margin on a cutting tool, nor is it suitable for this, since with the disclosed device the geometries required for margins on cutting tools, particularly in the case of tools with a plurality of cutting edges, can only be produced at excessively high time consumption and hence cost.